I implemented the idea I had, of using mem_itoa with base 100
and then printing two digits.
Omitting the strrev code to make everything equal, mem_toa is 64 bytes,
and the modified decimal-only version I call mem_tod is 80 bytes.
u64toa_nibbles is 90 bytes.
(That's assuming a ret of the reversed string or a 2-byte rjmp to
strrev; add 2 bytes if using JMP.)
Here's the timing:
Decimal Hex
Input mem_toa mem_tod itoa nibbles mem_toa itoa
8 bit 269 220 217 141 194 98
16 bit 664 462 451 321 527 187
24 bit 1294 783 838 608 1008 276
32 bit 2059 1219 1167 948 1637 365
40 bit 3059 1775 1649 1395 2414 454
48 bit 4194 2373 2127 1895 3339 543
56 bit 5477 3069 2733 2459 4412 632
64 bit 6995 3822 3420 3130 5633 721
mem_tod has the advantage that it does no multiplies, so it works fine
on all devices. The nibbles code is the fastest, and I haven't tried
to improve it yet.
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